This is the 308th most frequent Czech word.
druhou
The Czech word "druhou" means "second" (feminine accusative or instrumental form).
Here, 'druhou' is used as an ordinal adjective meaning 'second', describing the 'part of the book' as the one following the first one.
Přinesl jsem druhou část knihy.
I brought the second part of the book.
'Druhou' in this sentence describes the 'other side' as being the opposite of the one currently engaged or considered.
Otočil se na druhou stranu.
He turned to the other side.
In this case, 'druhou' indicates order, showing that it follows the first option in some sequencing or decision-making process.